Geography
Atmosphere and Pressure
The atmosphere is the layer of air surrounding the Earth. Its structure and pressure determine the weather.
Composition and layers
| Gas | Share |
|---|---|
| Nitrogen | about 78% |
| Oxygen | about 21% |
| Argon | about 0,9% |
| Carbon dioxide | about 0,04% |
- The most abundant gas: nitrogen (78%), not oxygen.
- Layers from bottom to top: troposphere, stratosphere, mesosphere, thermosphere, exosphere.
- Weather occurs in the troposphere. Its thickness is 8-10 km at the poles and 16-18 km at the equator.
- The ozone layer is located in the stratosphere.
Pressure
- Normal pressure: 760 mm Hg (about 1013 hPa), at sea level, at 0 °C.
- Pressure decreases by 1 mm every 10,5 m.
- Instruments: barometer (pressure), thermometer (temperature), hygrometer (humidity).
- Low pressure (cyclone): air rises, causing clouds and precipitation.
- High pressure (anticyclone): air sinks, and the sky is clear.
Temperature
In the troposphere, as altitude increases, the temperature drops by about 6 °C per 1 km.
Example: at sea level the pressure is 760 mm. At an altitude of 105 m: 105 ÷ 10,5 = 10, so 760 - 10 = 750 mm.
Cyclone: low pressure, precipitation. Anticyclone: high pressure, dry air.